We reported last month that that Natalie Portman (Black Swan, THOR) had been offered the lead role, opposite Robert Downey Jr. (Due Date, Untitled Sherlock Holmes Sequel) in Alfonso Cuarón‘s (Children of Men) new sci-fi project Gravity. The film was written by the director and his son Jonas Cuaron.

Now, THR reports that Warner Bros. and Portman are now in “active negotiations.” Robert Downey Jr. is set to play the leader of a team posted at a space station. While he and a female colleague (possibly Portman) are traveling outside the space station, the other team members are decimated by debris from an exploded satellite.

Gravity is slated to hit theaters in 2011.